This invention relates to pilot valve devices for regulating the flow of a fluid, and more particularly it is concerned with a pilot valve device of the type which is adapted to be brought to an open position in response to a mechanical signal so as to cause a compressed air to actuate an operating valve, wherein the operating valve can be actuated at high speed even if it is large in size.
A puffer type gas circuit breaker typifies the use of a pilot valve device for causing a fluid to actuate the operating valve in response to a mechanical signal. To meet an ever increasing demand for electric power by supplying electricity of high quality, there has in recent years been a growing demand for puffer type gas circuit breakers of extrahigh voltage and large capacity. Because of this, puffer type gas circuit breakers are required to operate at high speed by performing a two-cycle interruption, for example, in order to ensure transient security for the power system. Accordingly, the pilot valve device used with a puffer type gas circuit breaker for regulating the flow of a fluid is desired to have a construction such that it actuates the operating valve at high speed in response to a mechanical signal. On the other hand, the number of breaks per pole of circuit breakers increase when the circuit breakers are of extrahigh voltage. For example, the number of breaks per pole is generally four in the case of circuit breakers of a rated voltage of 550 KV. As a result, the weight of movable parts of the circuit breakers of this type has more than doubled that of movable parts of circuit breakers of a conventional 300 KV rating in which the number of breaks per pole is two. This necessitates the use of a larger operating force for actuating the circuit breakers, and consequently larger operating valves are required. However, conventional pilot valve devices are of a construction such that they are not suitable for actuating operating valves of a large size at high speed.
More specifically, the system which has hitherto been used for actuating the operating valve for a circuit breaker is as follows. A coil is excited by an electrical signal to disengage the hook of a hook mechanism by the magnetic force of the coil, so that a rod is actuated by the biasing force of a spring to apply a mechanical signal to a pilot valve to bring the same to an open position. Upon the pilot valve being opened, compressed air is caused to flow into the operating valve actuating chamber so as to drive an operating valve piston. If such system is used for actuating the aforesaid operating valve of a large size, a pilot valve of a larger size will be required. This in turn will make it necessary to use an operating spring of a larger biasing force for opening the pilot valve against the sealing pressure of a compressed fluid which is normally sealed in the pilot valve. An increase in the biasing force of the spring will result in an increase in the surface pressure of the engaging portion of the hook and also in an increase in the size of the hook. As a result, the moment of inertia of the pivotal movement of the hook will grow larger. Thus, technical difficulty will be encountered in causing the pilot valve of the prior art to operate at high speed.
Moreover, in the conventional pilot valve of the type described, upper and lower valve seats will necessarily have a small area if it is required to cause the pilot valve to operate at high speed while imparting to the pilot valve a valve seat pressure (usually 20 to 40 kg/cm.sup.2) which is necessary for sealing the compressed fluid within the pilot valve. The result of this is that the valve seats are relatively sharp in shape, thereby causing damage to packings with which the valve seats are brought into abutting engagement.